The interleukin 5 receptor alpha-subunit occurs either as a signalling, membrane-anchored isoform, or as a secreted, antagonistic variant. Given the key role of interleukin 5 in processes leading to differentiation and activation of eosinophils, a cell type critically involved in nasal polyposis, we will investigate this isoform expression pattern in human nasal polyposis in vivo and in vitro cell cultures.